1. Field of the Invention
This invention is related to the structure of a mirror box to be installed in a camera.
2. Description of Related Art
FIG. 4 shows a focal plane shutter system 11, a mirror box 3 and the front panel component 1 of a conventional camera. These elements are formed as independent units prior to being assembled in the camera. A lens installation mount 2 is provided on the front panel component 1. The mirror box 3 is installed behind the front panel component 1 (i.e., on the film surface side of the front panel component).
The mirror box 3 includes a side board 4, and a side bottom board 5, with a movable mirror 6 being placed between the boards 4 and 5. A light shielding paper 7 and a light shielding board 8 also are placed within the mirror box 3. The boards 4 and 5 are connected by an upper fixture 10. A maintenance component 9 for the optical viewfinder is placed in the top of the mirror box.
The focal plane shutter system 11 is placed behind the mirror box 3 (i.e., the side of the mirror box closest to the film surface). The focal shutter system 11 includes a primary plate 12 and a secondary plate 13, which are spaced apart by a specified interval, the components facing one another. A group of shutter blades 14 made of several thin, light shielding boards are provided between the primary plate 12 and the secondary plate 13. A shutter blade driving mechanism 15, for moving the group of blades 14 is placed in front (i.e., on the lens side) of the primary plate 12.
FIG. 5 shows a shutter plate 16 (or primary plate) of the focal plane shutter system disclosed in Utility Model Publication No. 63-45540 and U.S. Pat. No. 4,814,807, the shutter plate 16 being made of resin. The shutter plate 16 has an opening and support shafts 17 for mounting the blade driving mechanism, which are created of resin into one unit. The positions of the support shafts 17 are determined based on the center of the opening provided in the shutter plate 16. The starting position of the shutter blades are determined relative to the position of the support shafts.
With conventional products, however, the shutter system 11, the mirror box 3 and the front panel component 1 are created as independent units, as detailed above. Each component has the potential for causing an error (e.g. an installation error) during the camera assembly process. Due to these errors, a shift may occur between the center of the opening of the shutter plate 16 and the actual photographic light axis after assembly. Because of this, even if the shutter running curve, which runs inside the openings, is measured at a certain position based on the center of the opening in the independent shutter system, and if the shutter driving springs etc. are adjusted based upon such measurements, if the starting position of the shutter blade is set to prevent uneven exposure (in other words, the position of the support is adjusted) a problem occurs that the starting position, observed from the actual light axis (i.e., the photographic lens light axis) after camera assembly, may cause uneven exposure when there has been a shift between the relative positions of the photographic lens and the shutter system after assembly.
It is desirable that the slit forming section of the shutter blade be created in parallel, but in reality a slight shift occurs during manufacturing. The effect of such a shift is negligible when using a wide slit width (in the case of slow speeds), but when using a narrow slit width (high speeds) the slit width nearly disappears in certain sections of the screen, and sufficient exposure does not occur (i.e., uneven exposure is caused in the horizontal direction of the screen). This phenomena is especially likely to occur during the interval between the start-up of the shutter blades and the establishment of stable blade velocity (i.e., during the period of unstable blade velocity). Because of this, when the starting position of the shutter blades is slightly separated from the aperture, the shutter blades run through the aperture during the unstable time, resulting in an uneven exposure at the top of the screen. In order to prevent this uneven exposure, the starting position of the shutter blade is appropriately adjusted in a well known manner. However, as detailed above, even when the shutter blade (specifically, its support shaft) is adjusted to be at a position so as to prevent uneven exposure prior to assembling the shutter system to the camera, there is always a problem of the starting position being shifted after the assembly of the camera to a position that causes uneven exposure, due to the reasons detailed above (i.e., due to installation error).
Furthermore, with conventional systems, at least one or all of the components comprised of the mounting seat, the mirror box, and the shutter plate are made of metal, resulting in an increase in the weight of the camera.
Moreover, in a conventional system, the mounting seat, the mirror box, and the shutter plate are independent components, causing the number of components to increase, with an accompanying increase in cost and longer assembly time.